Coal-fired power generation equipment using a pulverized coal-fired boiler has occupied an important role due to, for example, a recent situation of escalating prices of petroleum and natural gas resulting from increased demand therefor. Conventionally, an air combustion boiler using air as combustion support gas has been generally used as a pulverized coal-fired boiler.
Coal combustion itself has a problem of much CO2 emission in comparison with petroleum or natural gas combustion. Thus, increased emission of CO2 due to increased dependence on coal fire power is a serious problem to be solved from a viewpoint of preventing global warming.
The air combustion boiler, which contains much nitrogen in flue gas, has a problem that troublesome is separation and withdrawal of nitrogen and CO2 from the flue gas.
Thus, an oxyfuel combustion boiler draws attention as means for substantially reducing CO2 emission to atmosphere and development thereof has been advanced.
Employed in the oxyfuel combustion boiler is flue gas recirculation in which most of combustion flue gas from the oxyfuel combustion boiler for burning pulverized coal is extracted midway from a gas flue; the flue gas extracted and mixed with oxygen produced in an oxygen production unit and adjusted to have a proper oxygen concentration is supplied as combustion support gas to the oxyfuel combustion boiler. According to the flue gas recirculation type oxyfuel combustion boiler, no nitrogen is contained in the flue gas to dramatically enhance a CO2 concentration in the flue gas finally discharged, which facilitates separation and withdrawal of CO2 from the flue gas.
There is, for example, the following Patent Literature 1 as a general conventional art literature pertinent to the oxyfuel combustion boiler as mentioned above.